It would be 90U (“U” = “upper”, or primary; “L” = “lower”,or secondary). Do you see a 21L or a 29L on there anywhere? That would represent the inset color.
You can go here to find the WA number:
https://www.autocolorlibrary.com/
Not to be a pedant here but a pic of the SPID or the truck would be super super helpful.
K